The efficacy and safety of a new antiallergic drug, intranasal azelastine (CAS 58581-89-8), in the treatment of seasonal allergic rhinitis was investigated in a 16 patient double-blind comparison with placebo and another 36 patient open comparison with budesonide (CAS 51333-22-3). Efficacy was assessed in terms of 13 signs and symptoms of allergic rhinitis and tolerability on the basis of spontaneously reported adverse events. In the first study, compared to placebo a one week's treatment with azelastine resulted in substantial relief of sneezing (p = 0.009), nasal itching (p = 0.009), swelling of the nasal mucosa (p = 0.067) and rhinorrhoea (p = 0.262) in patients having the above symptoms at baseline Of at least moderate to severe intensity. According to the judgement of the supervising physician, 718 azelastine-treated patients but none receiving placebo responded well to therapy (p = 0.001). In the second study a two weeks' treatment with intranasal azelastine was found not to differ significantly from budesonide. 67% of patients showed improvement in principal signs of rhinitis after one week's therapy irrespective of treatment. Nasal symptoms, including nasal obstruction, were most markedly improved by both treatments. Azelastine, but not budesonide, also relieved ocular symptoms associated with rhinitis. Adverse events did not occur more frequently under azelastine than under placebo treatment and were often of uncertain relationship to treatment.